The problems associated with adherence and growth of bacteria on medical devices are well know. For example, catheterization with a “central line catheter” involves placing a polyurethane or polyvinylchloride hose into a blood vessel in the patient's chest while the other end of the hose remains exposed to the hospital room environment and therefore to a variety of pathogens, potentially including drug-resistant pathogens. Frequently, this catheterization results in the life-threatening complication of system-wide infection of the blood. Research suggests that up to 90% of such cases originate in films of bacteria that adhere to catheter walls.
Other types of catheters that are frequently used include urinary catheters, which are typically used with incontinent elderly patients, and are typically made of silicone and latex. Unfortunately, virtually all patients who have urinary catheters in place for 28 days or more develop urinary tract infections. Nearly all hospital-acquired systemic infections that are not associated with central line catheters are associated with urinary catheters. Treatment of urinary catheter-associated infections alone costs an estimated $1.8 billion annually.
Similar problems currently exist with orthopedic implants. Main causes of orthopedic implant failure include host inflammatory responses, and infection due to the formation of bacterial biofilms on the surface of the implants. Furthermore, studies have shown that infections are very common at the site of pin insertion, and infection associated with external fixators may be as high as 85%. Because metal pins and wires are being used more often in the treatment of orthopedic trauma, primarily for external fixation of bone fractures, any device improvements that decrease the rate of infections from joint prostheses or other metallic implants could have a significant impact on the quality of orthopedic healthcare. Likewise, for ophthalmic devices, particularly contact lenses, microorganisms can adhere to the device during normal handling and wear, and even contaminate the storage container and/or solutions for cleaning or rehydrating such devices. While storage solutions have been developed to disinfect the device, the trend for contact lenses is to extend the period of time which they can be worn without taking them out for storage. Thus, a means directly associated with the ophthalmic device for decreasing the risk of infection, particularly in situations where the device is intended to be worn for more than one day or where it is impractical to remove the device daily for disinfection, is desirable.
A wide variety of surface modifications to medical devices have been tried with a goal of reducing infection rates of the modified medical devices. Such surface modifications include encapsulation of the medical device with a polymer to retard adherence by bacteria, and impregnation or coating of the medical device with antimicrobial agents. Representative examples of patents involving articles that have been coated or impregnated with anti-microbial drugs include U.S. Pat. No. 5,520,664 (“Catheter Having a Long-Lasting Antimicrobial Surface Treatment”), U.S. Pat. No. 5,709,672 (“Silastic and Polymer-Based Catheters with Improved Antimicrobial/Antifungal Properties”), U.S. Pat. No. 6,361,526 (“Antimicrobial Tympanostomy Tubes”), U.S. Pat. No. 6,261,271 (“Anti-infective and antithrombogenic medical articles and method for their preparation”), U.S. Pat. No. 5,902,283 (“Antimicrobial impregnated catheters and other medical implants”) U.S. Pat. No. 5,624,704 (“Antimicrobial impregnated catheters and other medical implants and method for impregnating catheters and other medical implants with an antimicrobial agent”) and U.S. Pat. No. 5,709,672 (“Silastic and Polymer-Based Catheters with Improved Antimicrobial/Antifungal Properties”).
However, the use of known antimicrobial coatings has been reported to have some disadvantages. For example, impregnating catheters with antibiotics may be counter-productive because the concentration of antibiotics released from the catheter inevitably falls, and bacteria are then exposed to sublethal levels of antibiotics. This results in a condition that can promote the development of antibiotic resistance. Coating the surface of a medical device with a polymer often requires special preparation of the surface, and multi-step chemical procedures. Another disadvantage of current methods to coat medical device surfaces is that, in general, the conditions necessary for attachment of the coating threaten to modify the relatively labile chemical groups or macromolecular folds that are typically desired for attachment of bioactive agents such as antimicrobial agents. The extra steps and costs necessary to preserve the function of bioactive agents in a surface coating often render the project cost-prohibitive.
Thus, the need remains in the art for a coating that can be applied to the surface of a medical device, wherein the coating inhibits adherence by microorganisms to, and/or growth of microorganisms on, the surface of the coated medical device.